A thesis submitted in partial fulfillment of the requirements for the degree of Ma ster of Science in Food Engineering and Bioprocess Technology, School of Environment, Resources and Development

Thesis (M. Sc.) - Asian Institute of Technology, 2016

The greatest hurdles that probiotic bacteria must overcome during feed processing, storage and in the upper gastrointestinal tract are acid and th e presence of bile. T he main purpose of this study was to develop a novel encapsulation techn i que to enhance the stability of thermal and acidic protection of probiotic bacteria. T hree encapsulating bio materials were considered as good potential carrier material s for encapsulating the L actobacillus strain namely Lactobacillus bulgaricus to protect from adverse environmental conditions. Capsules of alginate - whey protein isolate and alginate - resistant starch w ere produced at various concentrations and analyzed for thermal stress to be incorporated in poultry feed . A lginate - resistant starch capsules pr oved better viability at high processing temperature up to 90°C for 90 seconds . In this study , a disaccharide trehalose was also used to incorporate with alginate - resistant starch to increase the resistance to high temperature . Moreover, t he acid tolerance of the encapsulated cells was compared with the free cells in an in vitro gastric model and a significantly higher survival was recorded for encapsulated cells. A similar trend was observed in the presence of bile salts. Physical p roperties of alginate - re sistant starch capsules were also observed. The mean diameter of wet and freeze dried capsules of the combination of 2% (w/v) sodium alginate, 4% (w/v) resistant starch and 1% (w/v) trehalose were found to be in an acceptable range. The particles size had diameters of 1.71 ± 0.15 and 1.41 ± 0.12 mm for wet and freeze dried capsules , respectively. L. bulgaricus encapsulated with alginate - resistant starch - trehalose had higher ability of thermal protection at 90°C; viability was 2.84 Log CFU/g up to 90s for w et capsules than non - encapsulated bacteria l cell. A fter incubation in poultry simulated gastric fluid the viable count reduced from 8.51 to 5.20 log CFU/g for wet capsules whereas free cells were not detectable after 30 min of exposure. There was almost no detrimental effect of bile on encapsulated cells, 1.06 and 1.37 log CFU/g reductions in case of wet capsules for 1% a nd 2% (w/v) bile, respectively. The encapsulated L. bulgaricus released 7.99 log CFU/g viable cells in intestinal c olonic pH 6.8 within 2 h . Storage of encapsulated wet capsules at 37°C proved to be more detrimental to the entrapped cells than at 4°C.